Characterization of specific insulin-like growth factor (IGF)-I and IGF-II receptors on cultured rabbit articular chondrocyte membranes.

The interaction of insulin-like growth factor (IGF)-I and IGF-II with specific type-I and -II receptor sites on rabbit articular chondrocyte membranes was studied. With labelled IGF-I as tracer, half-maximal displacement of the label was obtained with 1.4 ng IGF-I/ml and 22 ng IGF-II/ml. Using IGF-II as labelled peptide. 16 ng unlabelled IGF-II/ml and 200 ng IGF-I/ml were needed to inhibit the binding by 50%. Covalent cross-linking experiments revealed the presence of typical type-I (Mr 130,000 under reducing conditions) and type-II (Mr 260,000) receptor sites. In addition, with 125I-labelled IGF-II a very intense labelled band appeared at Mr greater than 300,000. This band was not found in mouse liver membranes and human placental membranes.